In continuous feed systems, as utilized in industrial or municipal incinerators, waste material is continuously conveyed through the combustion chamber. Traditionally, the continuous feed incineration system has included a series of grates, which support the waste, and air is passed upwardly through the grates into contact with the waste material, while the ash and non-combustible materials pass downwardly through the grates and are collected in a water-filled trough. Waste is normally a low energy heat source, and as a result, certain materials, such as glass, plastic, and lower melting point metal alloys, will melt and form a slag which is apt to clog the grates and prevent air from passing through the grates into the mass of waste material. To counteract clogging, the conventional continuous feed system, as used in the past, has included a mechanism for agitating or moving the grates to dislodge the slag and to permit air to pass upwardly into the waste material.
Because of the problem in introducing adequate air through the grates into the waste material, the conventional continuous feed unit requires a relatively large volume conbustion chamber in order to adequately burn the combustible waste gases. Expensive and sophisticated controls are normally, required with the conventional continuous feed system in order to monitor various conditions in the system. Controls are required to monitor the air pressure in the combustion chamber to determine whether the grates are partially clogged, and to monitor the temperature in the combustion chamber and thereby control the air input through the grates to obtain proper burning. Because of the complexity of the controls, the cost of the conventional continuous feed incinerator is substantial.
More recently, a continuous feed incineration system, incorporating an auger combustor, such as that disclosed in U.S. Pat. No. 4,231,304, has been utilized. In this type of incinerator, a rotatable auger is mounted within a cylindrical combustion chamber and is conveyed through the combustion chamber and agitated by the auger. The ash and non-combustible materials are discharged from the opposite or downstream end of the combustion chamber, while the gases generated from the combustion process are passed through a heat exchanger and then discharged through a separator to the atmosphere.
As disclosed in the aforementioned patent application, the auger includes a tubular shaft and a hollow spiral flight which is carried by the shaft. Air is introduced into the downstream end of the hollow shaft and passes into an air passage which extends continuously through the spiral flight. The air is discharged from the flight into the combustion chamber through a plurality of ports formed along the length of the flight.
The auger acts to slowly convey and agitate the waste material, and air is discharged, not only within the mass of the combustible waste material, but is also discharged into the upper portion of the combustion chamber where it serves to burn the waste gases of combustion in a secondary combustion zone.
As disclosed in the aforementioned U.S. patent, the hollow auger flight is also provided with a cooling water passage which extends the length of the flight. Water is introduced into the water passage and serves to cool the auger. The water is heated as it passes through the water passage, and the heated water is discharged from the auger shaft and can be used for auxiliary heating purposes.